Fix issue trekhleb#315.

Author: trekhleb

src/data-structures/priority-queue/__test__/PriorityQueue.test.js

@@ -51,14 +51,16 @@ describe('PriorityQueue', () => {
     expect(priorityQueue.poll()).toBe(5);
   });
 
-  it('should be possible to change priority of internal nodes', () => {
+  it('should be possible to change priority of head node', () => {
     const priorityQueue = new PriorityQueue();
 
     priorityQueue.add(10, 1);
     priorityQueue.add(5, 2);
     priorityQueue.add(100, 0);
     priorityQueue.add(200, 0);
 
+    expect(priorityQueue.peek()).toBe(100);
+
     priorityQueue.changePriority(100, 10);
     priorityQueue.changePriority(10, 20);
 
@@ -68,14 +70,16 @@ describe('PriorityQueue', () => {
     expect(priorityQueue.poll()).toBe(10);
   });
 
-  it('should be possible to change priority of head node', () => {
+  it('should be possible to change priority of internal nodes', () => {
     const priorityQueue = new PriorityQueue();
 
     priorityQueue.add(10, 1);
     priorityQueue.add(5, 2);
     priorityQueue.add(100, 0);
     priorityQueue.add(200, 0);
 
+    expect(priorityQueue.peek()).toBe(100);
+
     priorityQueue.changePriority(200, 10);
     priorityQueue.changePriority(10, 20);